1. Field of the Invention
The present invention relates to an ultrasonic welding method for joining electric connection portions of single-core electric cables, twisted-wire electric cables, copper foils, etc.
2. Description of Related Art
Heretofore, the methods for joining electric connection portions of single-core electric cables, twisted-wire electric cables, copper foils, etc., included not only resistance welding but also ultrasonic welding. As shown in FIGS. 9 and 10, in a general ultrasonic welding apparatus, a welding head 12 is disposed at a forward end of a horn 1 projecting forward from an exciter unit U and downward from the horn 1, so that a top end of the welding head 12 serves as a welding tip (sonic pole) 11. An anvil 2 is provided so as to be opposite to the welding tip 11. In a situation where the subjects 13 are held between the welding tip 11 and the anvil 2, pressure is applied to the held portion and, at the same time, vibrational energy from an ultrasonic wave is applied to the welding tip 11 to make the welding tip 11 vibrate, thereby welding by vibrational heat (frictional heat) generated between the welding tip 11 and the subjects 13.
The ultrasonic welding has the advantage that no fragile product is generated in the joint portion between different kinds of metals. Consequently, a mother material is hardly damaged because the joining temperature is low compared with the resistance welding temperature. Thus, cost of welding is reduced.
The, ultrasonic welding, however, has a disadvantage that the adhesive strength, in particular the peel strength, is small compared with the resistance welding strength. This is because, in the case of the aforementioned ultrasonic welding apparatus 10, vibrational heat generated by the vibration of the welding tip 11 is local and low in energy so that the amount of heat is insufficient.
Having such an advantage as mentioned above, the ultrasonic welding method has been widely used for assembling various electronic parts. In recent years, however, with the increase in density of electronic parts used in a car, or the like, electric connection portions with higher reliability have been required. In particular, joined portions between terminals and electric wires, or the like, have been required to be fastened more securely.